From c99e4fac4ede7dbc9fd087e78165823a1bd253d5 Mon Sep 17 00:00:00 2001
From: Nuno Cruces <ncruces@users.noreply.github.com>
Date: Mon, 5 Dec 2022 13:24:58 +0000
Subject: [PATCH] List DisallowEmpty (windows).

---
 internal/win/user32.go |  1 +
 list.go                |  2 +-
 list_windows.go        | 32 +++++++++++++++++++++++++-------
 3 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/internal/win/user32.go b/internal/win/user32.go
index eb9fb68..59b52d6 100644
--- a/internal/win/user32.go
+++ b/internal/win/user32.go
@@ -142,6 +142,7 @@ const (
 	ES_AUTOHSCROLL = 0x0080
 
 	// List box control styles
+	LBS_NOTIFY      = 0x0001
 	LBS_EXTENDEDSEL = 0x0800
 
 	// Month calendar control styles
diff --git a/list.go b/list.go
index 732d1e5..f8ff565 100644
--- a/list.go
+++ b/list.go
@@ -57,7 +57,7 @@ func DefaultItems(items ...string) Option {
 	return funcOption(func(o *options) { o.defaultItems = items })
 }
 
-// DisallowEmpty returns an Option to not allow zero items to be selected (macOS only).
+// DisallowEmpty returns an Option to not allow zero items to be selected (Windows and macOS only).
 func DisallowEmpty() Option {
 	return funcOption(func(o *options) { o.disallowEmpty = true })
 }
diff --git a/list_windows.go b/list_windows.go
index 3e2f24b..3b97f13 100644
--- a/list_windows.go
+++ b/list_windows.go
@@ -31,17 +31,19 @@ func listDlg(text string, items []string, multiple bool, opts options) ([]string
 	}
 
 	dlg := &listDialog{
-		items:    items,
-		multiple: multiple,
+		items:         items,
+		multiple:      multiple,
+		disallowEmpty: opts.disallowEmpty,
 	}
 	return dlg.setup(text, opts)
 }
 
 type listDialog struct {
-	items    []string
-	multiple bool
-	out      []string
-	err      error
+	items         []string
+	multiple      bool
+	disallowEmpty bool
+	out           []string
+	err           error
 
 	wnd       win.HWND
 	textCtl   win.HWND
@@ -84,7 +86,7 @@ func (dlg *listDialog) setup(text string, opts options) ([]string, error) {
 		strptr("STATIC"), strptr(text), _WS_ZEN_LABEL,
 		12, 10, 241, 16, dlg.wnd, 0, instance, nil)
 
-	var flags uint32 = _WS_ZEN_CONTROL | win.WS_VSCROLL
+	var flags uint32 = _WS_ZEN_CONTROL | win.WS_VSCROLL | win.LBS_NOTIFY
 	if dlg.multiple {
 		flags |= win.LBS_EXTENDEDSEL
 	}
@@ -120,6 +122,7 @@ func (dlg *listDialog) setup(text string, opts options) ([]string, error) {
 		}
 	}
 
+	dlg.update()
 	dlg.layout(getDPI(dlg.wnd))
 	centerWindow(dlg.wnd)
 	win.SetFocus(dlg.listCtl)
@@ -166,6 +169,20 @@ func (dlg *listDialog) layout(dpi dpi) {
 	}
 }
 
+func (dlg *listDialog) update() {
+	if dlg.disallowEmpty {
+		var enable bool
+		if dlg.multiple {
+			len := win.SendMessage(dlg.listCtl, win.LB_GETSELCOUNT, 0, 0)
+			enable = int32(len) > 0
+		} else {
+			idx := win.SendMessage(dlg.listCtl, win.LB_GETCURSEL, 0, 0)
+			enable = int32(idx) >= 0
+		}
+		win.EnableWindow(dlg.okBtn, enable)
+	}
+}
+
 func listProc(wnd win.HWND, msg uint32, wparam uintptr, lparam *unsafe.Pointer) uintptr {
 	var dlg *listDialog
 	switch msg {
@@ -189,6 +206,7 @@ func listProc(wnd win.HWND, msg uint32, wparam uintptr, lparam *unsafe.Pointer)
 	case win.WM_COMMAND:
 		switch wparam {
 		default:
+			dlg.update()
 			return 1
 		case win.IDOK, win.IDYES:
 			if dlg.multiple {